U.S. patent application number 10/246739 was filed with the patent office on 2003-04-03 for mixed substance of triphenylamine dimers.
Invention is credited to Kita, Yoshio, Yamasaki, Yasuhiro.
Application Number | 20030064308 10/246739 |
Document ID | / |
Family ID | 19108188 |
Filed Date | 2003-04-03 |
United States Patent
Application |
20030064308 |
Kind Code |
A1 |
Kita, Yoshio ; et
al. |
April 3, 2003 |
Mixed substance of triphenylamine dimers
Abstract
The present invention intends to provide a TPD derivative being
excellent in electric properties as a compound due to its extremely
less content of impurities (TPD analogues) as well as being
excellent in film-forming property due to its low crystallinity.
The TPD derivative is a mixed substance of triphenylamine dimers
which contains at least the compound represented by formula B:
1
Inventors: |
Kita, Yoshio;
(Nishinomiya-shi, JP) ; Yamasaki, Yasuhiro;
(Neyagawa-shi, JP) |
Correspondence
Address: |
BIRCH STEWART KOLASCH & BIRCH
PO BOX 747
FALLS CHURCH
VA
22040-0747
US
|
Family ID: |
19108188 |
Appl. No.: |
10/246739 |
Filed: |
September 19, 2002 |
Current U.S.
Class: |
430/58.8 ;
252/500; 430/133; 430/59.4; 430/59.5; 430/73 |
Current CPC
Class: |
G03G 5/0517 20130101;
G03G 5/061443 20200501; G03G 5/05 20130101; G03G 5/0696 20130101;
C07C 211/54 20130101 |
Class at
Publication: |
430/58.8 ;
430/59.4; 430/59.5; 430/133; 430/73; 252/500 |
International
Class: |
G03G 005/047; H01B
001/00 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 19, 2001 |
JP |
2001-284953 |
Claims
What is claimed is:
1. A mixed substance of triphenylamine dimers which comprises at
least the compound represented by formula B. 6
2. A mixed substance of triphenylamine dimers which comprises the
compound represented by formula A, 7the compound represented by
formula B, 8 and the compound represented by formula C. 9
3. A mixed substance of triphenylamine dimers which is obtained by
allowing a mixture of 3-methyldiphenylamine and
4-methyldiphenylamine to react with 4,4'-dihalobiphenyl.
4. The mixed substance of triphenylamine dimers according to claim
3, wherein the 3-methyldiphenylamine and the 4-methyldiphenylamine
are mixed in a molar ratio of 75:25 to 95:5.
5. A charge-transporting material for a layered type
electrophotographic photoreceptor which comprises the mixed
substance of triphenylamine dimers according to any one of claims 1
to 4.
6. A charge-transporting layer for a layered type
electrophotographic photoreceptor which comprises the mixed
substance of triphenylamine dimers according to any one of claims 1
to 4 and a binder resin.
7. A process for forming a charge-transporting layer for a layered
type electrophotographic photoreceptor comprising the steps of:
dissolving the mixed substance of triphenylamine dimers according
to any one of claims 1 to 4 in a solvent together with a binding
resin; applying the resulting solution uniformly onto a
charge-generating layer, and drying the resulting coated layer.
8. A layered type electrophotographic photoreceptor which comprises
a conductive support, a charge-generating layer and a
charge-transporting layer, wherein the charge-transporting layer
comprises the mixed substance of triphenylamine dimers according to
any one of claims 1 to 4 as a charge-transporting material.
9. The layered type electrophotographic photoreceptor according to
claim 8, wherein the charge-generating layer comprises, as a
charge-generating material, a phthalocyanine compound selected from
the group consisting of titanyl phthalocyanine, .mu.-oxo-aluminum
phthalocyanine dimer and .mu.-oxo-gallium phthalocyanine dimer.
Description
BACKGROUND OF THE INVENTION
FIELD OF THE INVENTION
[0001] The present invention relates to triphenylamine dimer
derivatives useful for materials for electrophotographic
photoreceptors, organic electroluminescent (EL) materials and the
like. Particularly, the present invention relates to a mixed
substance of triphenylamine dimers capable of controlling its
crystallization during film formation when it is used for a thin
film of a charge-transporting layer of a layered type
electrophotographic photoreceptor.
[0002] Triphenylamine dimer (TPD) derivatives have been used as
materials for electrophotographic photoreceptors, organic
electroluminescent (EL) materials and the like. Particularly, they
are widely employed as charge-transporting materials (CTM) of
organic photoreceptors for electrophotography such as copy
machines, printers and the like or hole transporting materials
(HTM) in EL devices.
[0003] In the early stage of research, 4,4-TPD obtained by using
4-methyldiphenylamine as a raw material was used as such a TPD
derivative. However, there is a problem that when this is contained
practically in a thin film of a charge-transporting layer,
crystallization is liable to occur due to symmetrical structure of
4,4-TPD.
[0004] When a TPD derivative is used as a component of a layered
type photoreceptor, both the electric property of the TPD itself
and the film-forming property thereof are both important properties
for getting the best electric property. If crystals of TPD are
deposited in a film during a drying step and uniformity of the film
is lost, the electric property as a photoreceptor is deteriorated
obviously.
[0005] To solve the problem of poor film forming property of
4,4-TPD, 3,3-TPD obtained by using 3-methyldiphenylamine as a raw
material has come to be used widely. That is, by introducing the
methyl group into TPD at the m-position, symmetry of 3,3-TPD
(compound) is reduced to prevent crystallization when a solvent
dries. Further, addition of a small amount of 4,4-TPD to 3,3-TPD is
also made for that purpose.
[0006] On the other hand, for manufacturing TPD simply in high
yield, one of the present inventors has developed a novel method
for manufacturing 3,3-TPD (Japanese Patent Laid-Open Publication
No. 2000-256276 and U.S. Pat. No. 6,242,648). The 3,3-TPD obtained
in this method has high purity and is excellent in electric
property as a compound.
[0007] However, there has become apparent a new problem in that as
the purity of 3,3-TPD becomes higher, crystallinity of the compound
also becomes higher unfortunately and if this compound is
practically contained in a thin film of a charge-transporting
layer, film-forming property is deteriorated.
[0008] In other words, the reason why crystallization during film
formation has conventionally been controlled by using 3,3-TPD
probably is not the substitution with methyl at the 3-position, but
probably is that the amine employed as a raw material for
condensation, is a mixture of 3-methyldiphenylamine,
3,3'-dimethyldiphenylamine, diphenylamine and the like, and the
conventional 3,3-TPD contains a certain amount of TPD analogues
by-produced from them. On the other hand, these TPD analogues
deteriorate electric properties of an electrophotographic
photoreceptor as impurities.
SUMMARY OF THE INVENTION
[0009] The objective of the present invention is to provide a TPD
derivative being excellent in electric properties as a compound due
to its extremely less content of impurities (TPD analogues) as well
as being excellent in film-forming property due to its low
crystallinity.
[0010] The present invention provides a mixed substance of TPDs
which comprises at least the compound represented by formula B.
2
[0011] The term "mixed substance of TPDs" used in this
specification refers to a mixture substantially composed of
positional isomers of TPD represented by the chemical formula.
Thus, for example the above-mentioned TPD analogs are impurities of
the mixed substance of TPDs of the present invention, and it is
desirable that the content thereof is as small as possible.
[0012] A mixed substance of TPDs of the present invention
preferably contains the compound represented by formula A, 3
[0013] the compound represented by formula B, 4
[0014] and the compound represented by formula C. 5
[0015] The mixed substance of TPDs of the present invention is
excellent in electric properties as a charge-transporting material
and has low crystallinity. Thus, when a charge-transporting layer
of a layered type electrophotographic photoreceptor is formed by
using the mixed substance, a uniform, non-crystalline thin film is
provided (see FIG. 2) and a photoreceptor of high sensitivity is
provided.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] FIG. 1 is a graph showing the spectral sensitivities of the
photoreceptor pieces prepared in Examples 3, 4 and Comparative
Examples 5, 6, 7 and 8;
[0017] FIG. 2 is a microphotograph showing crystallization
condition of the charge-transporting layer of the photoreceptor
obtained in Example 4;
[0018] FIG. 3 is a microphotograph showing crystallization
condition of the charge-transporting layer of the photoreceptor
obtained in Comparative Example 5; and
[0019] FIG. 4 is a microphotograph showing crystallization
condition of the charge-transporting layer of the photoreceptor
obtained in Comparative Example 8.
DETAILED DESCRIPTION OF THE INVENTION
[0020] The mixed substance of TPDs of the present invention is
produced in the same method as that conventionally used for
production of TPD except that a mixture of 3-methyldiphenylamine
and 4-methyldiphenylamine is used as a raw material for reaction.
It is preferable to use a high-pure mixture of
3-methyldiphenylamine and 4-methyldiphenylamine which contains
impurities as small as possible. This is for the purpose of
controlling formation of the TPD analogues.
[0021] More preferably, the mixed substance of TPDs of the present
invention is produced in the same method as that described in
Japanese Patent Laid-Open Publication No. 2000-256276 where an
Ullmann reaction is employed.
[0022] That is, 4,4'-dihalobiphenyl, preferably,
4,4'-diiodobiphenyl represented by the following formula (1) is
obtained.
[0023] Next, a raw material amine mixture is obtained. The raw
material amine mixture is, as described above, a mixture of
3-methyldiphenylamine represented by the following formula (2) and
4-methyldiphenylamine represented by the following formula (3).
[0024] Each purity of 3-methyldiphenylamine and
4-methyldiphenylamine is preferably 97.5% by weight or more, more
preferably 99% by weight or more. If 3-methyldiphenylamine or
4-methyldiphenylamine has a purity of 95% by weight or less,
formation amounts of the TPD analogues will increase and electric
properties of the resulting TPD will be deteriorated.
[0025] The 3-methyldiphenylamine and the 4-methyldiphenylamine are
mixed in a molar ratio of preferably from about 75:25 to about
95:5, more preferably from about 90:10 to about 95:5. If the
combination amount of 4-methyldiphenylamine is more than 25% by mol
based on the amine mixture, 4,4-TPD is formed in large amount and
crystallization readily occurs during the formation of a
charge-transporting film in a photoreceptor. If the combination
amount of 4-methyldiphenylamine is less than 5% by mole based on
the amine mixture, the formation ratios of 3,4-TPD and 4,4-TPD are
low and it becomes difficult to obtain an objective mixed substance
of TPDs.
[0026] Next, the above-mentioned amine mixture is allowed to react
with 4,4'-diiodobiphenyl in the presence of a base, a copper
catalyst and a reaction promoter (e.g., polyethylene glycol).
[0027] In the reaction, as in the case of known Ullmann reactions,
as a base, alkali metal hydroxides such as potassium hydroxide and
sodium hydroxide; alkali metal carbonates such as potassium
carbonate and sodium carbonate; trialkylamines such as
triethylamine and triisopropylamine; and metal alkoxides such as
tert-BuONa and tert-BuOK are exemplified. From the viewpoint of
production cost (yield and cost of raw materials), potassium
carbonate is particularly preferred. Metal copper (Cu(0)) is used
as the copper catalyst. The amount of the base and the copper
catalyst may be the same as those employed in conventional Ullmann
reactions.
[0028] Polyethylene glycol or polyethylene glycol diether is used
as a reaction promoter or a reaction solvent. Preferable
polyethylene glycol includes diethylene glycol, triethylene glycol,
tetraethylene glycol and polyethylene glycol, or their mixtures and
the like. Specifically, PEG-6000 (trade name) manufactured by Wako
Pure Chemical Industries K.K. can be used. As polyethylene glycol
diether, for example, diethylene glycol dimethyl ether (diglyme),
triethylene glycol dimethyl ether (triglyme), tetraethylene glycol
dimethyl ether (tetraglyme), polyglyme and their mixtures,
diethylene glycol diethyl ether, and diethylene glycol methyl ethyl
ether and the like are exemplified. Specifically, PMP400 (trade
name) manufactured by Toho Chemical Industry K.K. can be used.
[0029] The amount of a reaction promoter to be used is from
{fraction (1/10)} to 10 times, preferably from {fraction (1/10)} to
1/5 times by weight based on the weight of 4,4'-diiodobiphenyl.
[0030] The reaction between 4,4'-diiodobiphenyl and the amine
mixture (N-arylation reaction) may be carried out using, as a
reaction solvent, polyethylene glycol or polyethylene glycol
diether, which is a reaction promoter, or may be carried out using
other proper reaction solvents. It may also be carried out without
using any solvent. The reaction procedure generally comprises
charging 4,4'-diiodobiphenyl, a raw material amine mixture, a base
(preferably potassium carbonate), a copper catalyst, a reaction
promoter and, optionally, a reaction solvent into a proper vessel
and stirring for 5 to 40 hours while holding at 100 to 250.degree.
C.
[0031] The progress of the reaction can be traced by conventional
methods such as chromatography. After the completion of the
reaction, the solvent is removed by distillation and products are
separated and purified by conventional methods such as
chromatography. The products can be identified by elementary
analysis, MS (FD-MS) analysis, IR analysis, .sup.1H-NMR and
.sup.13C-NMR.
[0032] Next described is a typical example of the process of the
production of the mixed substance of TPDs of the present
invention.
[0033] To a mixture of 3-methyldiphenylamine and
4-methyldiphenylamine in a molar ratio of about 90:10 to 95:5, a
copper catalyst (copper powder) is added and heated to about
30.degree. C. To the resulting mixture, 4,4'-diiodobiphenyl and
polyethylene glycol (PEG) as a reaction promoter are added and
heated to 100.degree. C. Then, powdery potassium carbonate is
added, heated to 205.degree. C. and stirred for 14 hours.
[0034] After standing to cool, DMF is added and stirred at
130.degree. C. for 1 hour. After additional standing to cool to
90.degree. C., hot water is added to the resulting mixture and is
stirred for additional 2 hours. After filtration, the resulting
cake is washed with hot water to obtain brown solid.
[0035] Purification is carried out by dispersing and stirring the
resulting brown solid in DMF for about 1 hour and then separating
solid by filtration.
[0036] The resulting cake is further washed with DMF and methanol.
After refluxing the resulting solid together with active carbon in
xylene for about 1 hour, the mixture is allowed to cool to
70.degree. C. and subsequently is filtered.
[0037] The filtrate is passed through a column filled with an
absorbent to obtain a colorless, transparent solution. The solvent
is removed by distillation under reduced pressure. The crystals
deposited are collected by filtration and dried to obtain a
composition of positional isomeric TPDs of the present invention in
high yield.
[0038] The mixed substance of TPDs produced in this method
theoretically is a mixture of three kinds of TPD derivatives
represented by formulae A, B and C above.
[0039] The formation ratio of the above three TPD derivatives is
about 81:18:1 according to the probability when the compounding
ratio of 3-methyldiphenylamine and 4-methyldiphenylamine is 90:10
by mol, and is 90.25:9.5:0.25 when the compounding ratio of
3-methyldiphenylamine and 4-methyldiphenylamine is 95:5 by mol.
[0040] 4,4-TPD (formula C) is liable to form crystals because of
its symmetrical structure. Therefore, amorphism of a
charge-transporting film may be impaired in the case when content
of the 4,4-TPD is high level. However, according to the above
described process, the formation probability of 4,4-TPD is 10% or
several percent or less in the mixed substances of TPDs, and
amorphism of the film is not impaired.
[0041] Next, examples of the application of the mixed substance of
TPDs obtained in the method of the present invention for layered
type electrophotographic photoreceptors will be described.
[0042] An electrophotographic photoreceptor is a device such that
when a beam light corresponding to an image is applied thereto, a
latent image consisting of charges is formed on the surface where
the light is received. An organic electrophotographic photoreceptor
comprises an organic photoconductive material on a conductive
support. The organic photoconductive material is a material formed
by binding a photoconductive compound with a resin.
[0043] In general, as electrophotographic photoreceptors, layered
type photoreceptors are widely employed. The layered type
photoreceptor comprises a charge-generating layer containing a
charge-generating material, such as phthalocyanines, which
generates charges when light is applied thereto, and a
charge-transporting layer containing a charge-transporting material
which transports charges to a surface region of the
photoreceptors.
[0044] TPD derivatives are useful as charge-transporting materials
of electrophotographic photoreceptors which are employed widely in
copy machines or the like employing the electrophotography
technology. Particularly, the mixed substance of TPDs of the
present invention provides photoreceptors having good electrostatic
property and also having medium or high sensitivity and high
durabilities (durabilities with respect to sensitivity and
potential) when it is used in a charge-transporting layer of an
organic photoreceptor in combination with phthalocyanine-type
charge-generating materials such as titanyl phthalocyanine,
.mu.-oxo-aluminum phthalocyanine dimer and .mu.-oxo-gallium
phthalocyanine dimer.
[0045] Such a function separation type photoreceptor is formed, for
example, by laying a charge-generating layer and a
charge-transporting layer, both being in the form of a thin film,
onto a conductive support. Metal such as aluminum and nickel,
metallized films and the like can be used as a substrate of the
conductive support. The substrate may be produced in the form of
drum, sheet or belt.
[0046] The TPD derivatives may be applied to the organic
photoreceptors for electrophotography such that a charge-generating
layer containing a photoconductive phthalocyanine pigment as a
charge-generating material is formed in the form of a thin film on
a conductive support. The charge-generating layer is generally
formed by preparing an application liquid in which a
charge-generating material is dispersed in a solution of a binding
resin dissolved in a solvent, and subsequent applying the
application liquid onto a conductive support. However, the
charge-generating layer may be formed by vapor deposition of a
phthalocyanine pigment onto a conductive support to form a thin
film.
[0047] The phthalocyanine pigments may be dispersed in the method
conventionally known to the art by using a ball mill, a sand mill,
a paint shaker and the like.
[0048] The means for applying a charge-generating layer is not
particularly limited. For example, a bar coater, a dip coater, a
spin coater, a roller coater and the like can properly be used.
Drying can be carried out at a temperature of 30 to 200.degree. C.
for a period of 5 minutes to 2 hours, at rest or under
ventilation.
[0049] The solvent for the application liquid is not particularly
limited on condition that the phthalocyanine pigment is uniformly
dispersed without being dissolved and the binding resin optionally
used is dissolved. Examples thereof include alcoholic solvents such
as methanol, ethanol, isopropanol and butanol; aromatic solvents
such as toluene, xylene and tetralin; halogen-containing solvents
such as dichloromethane, chloroform, trichloroethylene and carbon
tetrachloride; ester solvents such as ethyl acetate and propyl
acetate; ether solvents such as ethylene glycol monoethyl ether,
dioxane and tetrahydrofuran; ketone solvents such as cyclohexanone,
methyl ethyl ketone and methyl isobutyl ketone; dimethylformamide,
dimethyl sulfoxide and the like.
[0050] The binding resin can be selected from a wide range of
insulating resins. Preferred resins include condensation-type
resins such as polycarbonate, polyester, polyamide and polyarylate;
addition polymerizates such as polystyrene, polyacrylate,
styrene-acrylic copolymers, polyacrylamide, polymethacrylate,
polyvinyl butyral, polyvinyl alcohol, polyacrylonitrile,
polyacryl-butadiene copolymers, polyvinyl chloride and vinyl
chloride-vinyl acetate copolymers; organic photoconductive resins
such as poly-N-vinylcarbazole and polyvinylanthracene; polysulfone,
polyether sulfone, silicone resins, epoxy resins and urethane
resins. These may be used in proper combination.
[0051] The binding resin is employed in an amount of 0.1 to 3 ratio
by weight based on the weight of the charge-generating material. If
the amount is greater than 3 ratio by weight, concentration of the
charge-transporting material in the charge-generating layer becomes
small and photosensitivity becomes poor. The charge-generating
layer generally has a thickness of 10 .mu.m or less, preferably
from 0.05 to 5.0 .mu.m.
[0052] Next, a charge-transporting layer containing a
charge-transporting material is formed in the form of a thin film
on the charge-generating layer. The charge-transporting layer may
be applied in the same manner as that described for the
charge-generating layer. The thin film can be formed, for example
by dissolving a charge-transporting material in a solvent
optionally together with a binding resin, applying the resulting
solution uniformly onto the charge-generating layer and then
drying.
[0053] As the charge-transporting material, the mixed substance of
TPDs obtained in the method of the present invention is used. As
the binding resin and the solvent for forming the
charge-transporting layer, the same materials as that described for
the charge-generating layer can be used.
[0054] The binding resin is employed in an amount of from 0.1 to 5
ratio by weight based on the weight of the charge-transporting
material. If the amount is greater than 5 ratio by weight,
concentration of the charge-transporting material in the
charge-transporting layer becomes small and photosensitivity
becomes poor. The charge-transporting layer generally has a
thickness of 100 .mu.m or less, preferably from 5 to 50 .mu.m.
[0055] The following Examples further illustrate the present
invention in detail but are not to be construed to limit the scope
thereof.
EXAMPLE 1
Synthesis of Mixed Substance of TPDs
[0056] To 5000-ml four-neck flask, 438 g (2.43 mol) of
3-methyldiphenylamine and 49 g (0.27 mol) of 4-methyldiphenylamine
(molar ratio=90:10) were fed. 28 g (4.4 mol) of copper powder was
added thereto and was heated to 30.degree. C. To the mixture, 450 g
(1. 1 mol) of 4,4'-diiodobiphenyl and 47 g of PEG6000 were added.
After heating to 100.degree. C. and adding 307 g (2.2 mol) of
powdery potassium carbonate, the resulting mixture was heated to
205.degree. C. and stirred for 14 hours. After standing to cool,
DMF was added and stirred for 1 hour at 130.degree. C. After
standing to cool to 90.degree. C., hot water was added to the
resulting mixture and was stirred for additional 2 hours. After
filtration, the cake was washed with hot water to obtain a brown
solid. The resulting brown solid was dispersed and stirred in DMF
for 1 hour and then collected by filtration. Further, the resulting
cake was washed with DMF and methanol. The resulting solid was
refluxed together with active carbon in xylene for 1 hour,
subsequently allowed to cool to 70.degree. C. and then filtered.
The filtrate was passed through a column filled with an absorbent
to obtain a colorless transparent solution. The solvent was removed
by distillation under reduced pressure. The crystals deposited were
collected by filtration and were dried to obtain 455 g of the mixed
substance of TPDs.
EXAMPLE 2
Synthesis of Mixed Substance of TPDs
[0057] 457 g of the mixed substance of TPDs was obtained in the
same manner as that described in Example 1 except that the mixing
ratio of 3-methyldiphenylamine to 4-methyldiphenylamine was changed
to 95:5 by mol.
EXAMPLE 3
Preparation of Layered Type Photoreceptor Piece
[0058] In a 100-ml mayonnaise bottle, 0.2 g of Y-type titanyl
phthalocyanine (a product obtained by the manner as described in
Japanese Patent Laid-Open Publication No. H3(1991)-35064), 0.2 g of
the polyvinyl butyral resin (trade name: Elex BH-3, manufactured by
Sekisui Chemical K.K.), 59.6 g of cyclohexanone and 50 g of 3 mm
.phi. glass beads were added and shaken with a paint shaker for 1
hour. The resultant was formed into a film to have a thickness of
0.5 .mu.m on an aluminum plate washed well with acetone by use of a
bar coater No. 6. Thereby, a charge-generating layer was formed.
Further, a solution obtained by dissolving 1.0 g of the mixed
substance of TPDs synthesized in Example 1 and 1.0 g of
polycarbonate (trade name: Panlite L-1250, manufactured by Teijin
K.K.) in 11.3 g of dichloromethane was formed into a film to have a
thickness of 20 .mu.m on the charge-generating layer by use of a
bar coater No. 32. Thereby, a charge-transporting layer was formed.
Thus, layered type photoreceptor was prepared.
EXAMPLE 4
Preparation of Layered Type Photoreceptor Piece
[0059] A layered type photoreceptor piece was prepared in the same
manner as that described in Example 3 except that the mixed
substance of TPDs synthesized in Example 2 was used.
Comparative Example 1
Synthesis of 3,3-TPD (Method described in Japanese Patent Laid-Open
Publication No. 2000-256276)
[0060] To a 100-ml four-neck glass flask, 1.0 g (2.46 mmol) of
4,4'-diiodobiphenyl and 20 ml of o-dichlorobenzene were added.
Further, 1.08 g (5.90 mmol) of 3-methyldiphenylamine, 0.104 g of
polyethylene glycol (PEG-6000 (trade name) manufactured by Wako
Pure Chemical Industries K.K.) as a reaction promoter, 2.73 g
(0.0198 mol) of potassium carbonate and 0.635 g (9.87 mmol) of
copper (powder) were added and refluxed under stirring. The
reaction was traced by high-performance liquid ion chromatograph
and the refluxing was continued under stirring until the peaks of
the raw materials and intermediates had disappeared (for 22 hours).
After hot filtration, the product was washed with dichloromethane
until the color of the filtrate had become light and then the
solvent was removed under reduced pressure. The residue was
purified by silica gel chromatography to obtain 1.01 g of
N,N'-diphenyl-N,N'-ditol- yl-4,4'-diaminobiphenyl (3,3-TPD)
(yield=78.7%).
Comparative Example 2
Synthesis of 4,4-TPD
[0061] 4,4-TPD was synthesized in the same manner as that described
in Comparative Example 1 except that 4-methyldiphenylamine was used
in place of 3-methyldiphenylamine.
Comparative Example 3
[0062] A simple mixture of TPD was obtained by mixing 3,3-TPD
synthesized in Comparative Example 1 and 4,4-TPD synthesized in
Comparative Example 2 by mol of 90:10.
Comparative Example 4
[0063] A simple mixture of TPD was obtained by mixing the 3,3-TPD
synthesized in Comparative Example 1 and the 4,4-TPD synthesized in
Comparative Example 2 by mol of 95:5.
Comparative Example 5
[0064] A photoreceptor piece was prepared in the same manner as
that described in Example 3 except that the 3,3-TPD synthesized in
Comparative Example 1 was used in place of the mixed substance of
TPDs.
Comparative Example 6
[0065] A photoreceptor piece was prepared in the same manner as
that described in Example 3 except that the 4,4-TPD synthesized in
Comparative Example 2 was used in place of the mixed substance of
TPDs.
Comparative Example 7
[0066] A photoreceptor piece was prepared in the same manner as
that described in Example 3 except that the simple mixture of TPD
prepared in Comparative Example 3 was used in place of the mixed
substance of TPDs.
Comparative Example 8
[0067] A photoreceptor piece was prepared in the same manner as
that described in Example 3 except that the simple mixture of TPD
prepared in Comparative Example 4 was used in place of the mixed
substance of TPDs.
Test of Electric Properties
[0068] The organic photoreceptor property and the spectral
sensitivity were measured by using an electrostatic paper analyzer
(trade name: EPA-8200, manufactured by Kawaguchi Electric Works
K.K.). The results are shown in Table 1.
1 TABLE 1 Dark Half decay Residual Conditions of TPD decay rate
exposure potential synthesis V.sub.max (V) (%) sensitivity (Lx.s)
(V) Example 3 3-MPA:4-MPA = -580 -22.3 1.12 -2.3 90:10 Example 4
3-MPA:4-MPA = -634 -23.2 1.07 -3.0 95:5 Comp. 3-MPA = 100% -587
-22.1 1.12 0 Example 5 Comp. 4-MPA = 100% -498 -28.6 0.90 -1.7
Example 6 Comp. 3,3-TPD (90%) + -475 -29.9 1.05 -2.3 Example 7
4,4-TPD (10%) Comp. 3,3-TPD (95%) + -624 -20.1 1.20 -9.3 Example 8
4,4-TPD (5%) MPA: Methyldiphenylamine
[0069] The graphs of spectral sensitivity of Examples 3 and 4 and
Comparative Examples of 5, 6, 7 and 8 are shown in FIG. 1.
[0070] Considerations: In the graphs of spectral sensitivity,
Examples 3 and 4 are relatively high, whereas Comparative Examples
7 and 8 which employ the simple mixture of TPD are relatively low.
As to Comparative Example 6, the poor sensitivity is probably due
to impaired uniformity of the film caused by crystallization of
4,4-TPD which has good symmetrical structure. In Comparative
Example 5, conventional 3,3-TPD was used and properties
corresponding thereto were shown.
Film-forming Property
[0071] The photoreceptor piece used for the test of electric
properties was stripped off from the aluminum plate and was
observed with an optical microscope BX60 (OLYMPUS; magnifications:
eye lens=.times.10, object lens=.times.10) equipped with a digital
camera HC2500 (FUJIX) using transmitted light. Analysis and print
were carried out by using the image analysis software "analy SIS
3.1 (Soft-imaging System)".
[0072] The microphotographs (magnification: .times.100) obtained
with respect to the photoreceptors of Example 4 and Comparative
Examples 5 and 8 are shown in FIGS. 2, 3 and 4, respectively. In
the photographs, black parts are crystalline parts where
crystallization occurred.
[0073] Considerations: In Example 4 (FIG. 2), there are at least
some crystalline parts, but remarkable improvement was observed by
comparison with Comparative Example 5 (FIG. 3). In Comparative
Example 8 (FIG. 4), a considerable improvement was observed by
comparison with Comparative Example 5 (FIG. 3), but is not
satisfactory.
* * * * *